Hong Kong authorities started on Thursday clearing the main pro-democracy protest site that has choked roads into the city's most economically and politically important district for more than two months as part of a campaign to demand free elections.

The mainly peaceful protests in the Chinese-controlled city have represented one of the most serious challenges to China's authority since the 1989 pro-democracy demonstrations and bloody crackdown in and around Beijing's Tiananmen Square.

Hundreds of police stood by in the Admiralty district next to government buildings and the Central business area as workers in construction hats used wire cutters to remove barricades erected by protesters after a court injunction two days ago.

"Everyone should follow the court order and leave immediately," a bailiff said.

There was little initial resistance as scores of protesters packed up pillows, blankets and other belongings from inside their tents and prepared to leave.

"Some of my friends are prepared to stay till the last moment, but I will walk away," said 20-year-old student Lucy Tang. "I will for sure miss this place. It has become my home."

For many, it was a tearful farewell as they waved goodbye to the site where thousands had gathered in recent weeks. Others said the protests had injected life into the former British colony's democracy movement.

"The movement has been an awakening process for Hong Kong. People who weren't interested in politics before are now and aren't afraid to get arrested, especially the young people," said Labour Party lawmaker Lee Cheuk-yan.

"The democracy movement is filled with energy. It's the passing of the torch from one generation to the other."

"We'll be back"

A large yellow banner bearing an umbrella and the words "We'll be back" was draped in the centre of the highway where protesters have camped out, with similar messages scrawled on roads and posted on tents.

Next to the Chinese People's Liberation Army (PLA) base in the heart of the city, a huge orange banner erected across barricades read: "It's just the beginning."

Hong Kong Federation of Students leader Alex Chow said the clearance was not the end of the movement.

"You might have the clearance today but people will come back on to the streets another day," Chow said.

Hong Kong media magnate Jimmy Lai, an outspoken critic of Beijing who has backed pro-democracy activists through his publications and with donations, sat near the PLA base with a "Keep Calm and Stay Peace" sign leaning against his knee.

Some 7,000 police officers were due to be deployed in two shifts to handle the clearance, Hong Kong media reported.

People at some supply stations were bracing for possible clashes with police, laying out boxes of goggles and umbrellas for students to protect themselves against any use of pepper spray or batons by police.

The Admiralty site has stood as a poignant symbol of calls for democracy that have been spurned by the government and Communist Party rulers in Beijing.

Hundreds of tents have dotted the eight-lane highway that connects some of the city's most important financial and commercial districts since late September.

The protest site had taken on an almost village feel, with a large study area, first aid tents and scores of supply stations scattered across the highway.

More than 10,000 people massed at the protest site on Wednesday evening, even as authorities warned people to stay away, before the final clearance.

Hong Kong returned to Chinese rule in 1997 under a "one country, two systems" formula that gives the city more autonomy and freedom than the mainland and a goal of universal suffrage.

The protesters are demanding open nominations in the city's next election for chief executive in 2017. Beijing has said it will allow a vote in 2017, but only between pre-screened candidates.